Life history characteristics of an evergreen herbaceous perennial, Heloniopsis orientalis, were compared in two neighboring populations under different environments in Toyama prefecture on the Japan Sea side of central Japan. One was a population on a shady forest floor, which is the typical habitat of this species, and the other was a population on a slope along a sunken road. On the forest floor, no seedlings of H. orientalis were evident, and the population seemed to be maintained by vegetative reproduction involving plantlets formed at the tips of leaves. In the other population observed on the steep slope, most of the individuals replaced their leaves every year, and therefore plantlets could not grow. This population seemed to be maintained exclusively by sexual reproduction. Differences were also observed in the plant size of individuals possessing flower buds ; individuals of the slope population flowered at an earlier developmental stage than those of the forest floor population. This may be adaptive, since unstable and disturbed conditions on the slope could favor early maturity. The difference in reproductive behavior, i. e. vegetative reproduction on the forest floor and sexual reproduction on the slope, may also reflect the ecological differentiation observed in the two wild populations.
X-ray fluorescence analysis (XRF) has been widely used for elemental analysis in the field of quality control and research, since it allows non-destructive analysis and sample preparation is easy. In general, quantitative analysis is carried out using a calibration curve obtained from many standard samples. However, for some applications such as analysis of plant samples, it may be difficult to prepare standard materials. The recent development of the fundamental parameter method (FP method) makes it possible to perform quantitative analysis using only a few standards or reference samples. In the qualitative analysis program, semiquantitative results can be calculated using the X-ray intensities for the detected elements. The recent application of XRF to plant analysis using the FP method is discussed.
A number of studies have found evidence to suggest that an increase in the level of air pollution, including acidic precipitation, could be related closely to changes in the patterns of insect attack on forest trees. The present article reviews current knowledge on the effects of airpolluted environments on phytophagous insect populations and the underlying mechanisms involved. Many field observations carried out along pollution gradients have found a general trend for increases in the density of phytophagous insects, particularly sap-feeders such as aphids, in zones with high and / or intermediate levels of pollution, although the response differs among insect species. Experimental studies have revealed that increased growth and reproduction in phytophagous populations on plants prefumigated with gaseous pollutants such as SO2,O3 and oxides of nitrogen, are probably attributable to changes in the nutritional value and the level of secondary metabolites as allochemicals in the plants. Most of the results of recent studies using either approach have strongly suggested that air pollution has a dual effect of increasing the palatability of the plants to insects and reducing parasitism and predation, which may partly account for the causal mechanisms of outbreaks of phytophagous insects in forests.
An increasing number of studies on insect-plant relationships are providing a large volume of information indicating the variability and flexibility of species interactions that are important for improvement of biodiversity. Recent studies on plant-mediated species interactions of herbivorous insects have revealed that interspecific interactions are often indirect, asymmetrical and subtle, and that morphological, phenological, and chemical changes in the host plant alter the success of predation or parasitism by natural enemies. Even insects feeding at different times or on different parts of a plant may have a substantial effect on the quality or quantity of resources available to one another. Three-trophic-level interactions have recently received much attention in insect-plant interactions, addressing a significant role of natural enemies as part of a plant's battery of defenses against herbivores. It is also recognized that changes in host plant quality affect the efficacy of parasitoids or predators directly or indirectly by altering insect host location or vulnerability. Interactions between temporally separated guilds may play a critical role in distribution and survivorship, and thus the population dynamics of insect herbivores. There is evidence to support the view that one species attacking a host plant early in the season can change the performance or abundance of another species attacking late in the season, through changes in host quality. Similarly, this notion is applicable to the situation of spatially separated guilds that utilize different parts of the shared host plant in very different manners ; for example one attacking leaves and the other roots. Such interactions among temporally or spatially separated guild members sharing the same host plants are often asymmetrical.
Microbial organisms cultured in the laboratory provide a useful tool for analyzing the process of evolution through natural selection. Various mutants arise in a given microbial population, and some of them increase in frequency, replacing previous clones ("periodic selection"). Although there have been a number of studies on changes in the genetic composition of bacterial populations in long-term culture, the ecological mechanisms operating in such replacement during natural selection are less known. This article reviews current knowledge of experimental evolution in the laboratory, focussing particularly on how and why a new mutant replaces previous types. Exploitative competition, interference competition, and predator-mediated (apparent) competition can work as causal mechanisms of replacement, through which an increase of a mutant leads to decreases in the density of previous types. In exploitative competition, a mutant with a higher growth rate and / or lower mortality reduces a resource equilibrium, which, in turn, has a negative effect on the net growth rate of the old types. In interference competition, an increase in a mutant causes a decrease in previous types through direct or indirect inhibition via metabolites. In predator-mediated (apparent) competition, a mutant with a higher growth rate and / or lower predation rate raises the predator equilibrium density, which, in turn, has a negative effect on the net growth rate of the old types. Experimental evidence supports the operation of natural selection through these three negative interactions. However, more experimental studies on the ecological interactions generating evolutionary forces are required for further understanding of evolution through natural selection.
Pinus pumila grows in alpine regions from central Japan to eastern Siberia and generally forms dwarf scrub. The ecological features of P. pumila were reviewed, focusing especially on its dry matter production and process of regeneration. Some aspects related to dry matter production, e. g., canopy structure, leaf longevity, phenology, litterfall and photosynthesis, were discussed in comparison with those of other forest types including Pinus species. Based on the annual above-ground net production and gross production of the pine forest, the carbon allocation pattern and efficiency of energy fixation were also discussed. The reproduction style of P. pumila is characterized by two different phases : seedling establishment as a result of seed dispersal by nutcrackers, and regeneration by layering in the mature trees. The ecological characteristics of dry matter production and the regeneration process were discussed in relation to the survival of P. pumila.